The field of the invention relates generally to electric motors, and more specifically, to methods and systems for envelope and efficiency control in motors using low capacitance.
Typical electric motor systems include a motor drive controller and an electric motor. The motor drive controller receives power from an alternating current (AC) power supply, and applies the power to a rectifier and to capacitors to generate a smoothed direct current (DC) voltage. The motor drive controller then supplies a chopped DC voltage to the electric motor through an inverter, which uses the power to drive a load.
Capacitors typically used in motor drive controllers include electrolytic capacitors with high capacitances (about several hundred μF). The high capacitances cause the capacitors of the motor drive controller to be large and expensive. Such capacitors may necessitate a larger motor drive controller and may reduce the lifespan of the motor drive controller. New drive technologies target having substantially reduced capacitance capacitors to reduce the size and expense of the motor drive controller. However, as the energy storage elements (capacitors) have been reduced in the motor drives controllers, motor phase currents may not reach typical steady state waveforms and torque production may have a ripple component that varies in amplitude as a function of a motor load point and an input voltage to the motor drive controller. Typical control algorithms regulating steady state motor currents cannot deliver constant average torque performance or a constant average flux value, which is related to the efficiency of the electric motor. Accordingly, implementing a typical control algorithm in a motor drive controller that does not include one or more electrolytic capacitors with high capacitances (several hundred μF) may result in a loss of torque, efficiency, and envelope control.